QGIS » QGIS Application

The "old zoomed map -> blank -> new map" is not something specific to raster layers, it may happen also with vectors, it is just more obvious with rasters. The behaviour will need some updates to make better impression. The reason for it is that first 250 ms, the canvas shows previously rendered map transformed to the new extent (e.g. zoomed in). Then, the old map is replaced with preview of newly rendered map - which may be still blank at that point, giving the resulting effect. In the meantime you could increase the refresh ration in Options to a greater value to remove the effect.

Regarding faster/slower rendering, could you provide approximate timings of 2.2 vs 2.3 ? Also, we would need the data you used for the comparison.

Rendering speed:

Used the DEM+HDF files available at http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/
Set project to EPGS 32661 (enabled on-the-fly projection), setting one extent covering the whole dataset in the left part of the canvas, another extent to the right part. Then using Zoom last / Zoom next for repeated tests.

Produced these averages:
QGIS2.2: 2.7 sec.
QGSI2.3: 4.3-5.3, most results above 5 sec.

Then using Zoom last / Zoom next for repeated tests.

here (Linux) it takes no time in zooming_in_out/last/next on both 2.2 and master

maybe it's due to different settings, make sure they bot have rendering cache turned on (or off)

It's evident with any raster here. And regardless of map update interval settings. Cache settings are the same in both 2.2 and 2.3 (off). (It also reproduces when on-the-fly reprojection is turned off) ...

andskog - wrote:

It's evident with any raster here. And regardless of map update interval settings. Cache settings are the same in both 2.2 and 2.3 (off). (It also reproduces when on-the-fly reprojection is turned off) ...

then better to attach here a full project and/or a screencast (to try better understand your issue).